Monte Carlo N-Particle eXtended Research Articles

The radiation fields around a proton therapy facility: A comparison of Monte Carlo simulations

A proton therapy test facility with a beam current lower than 10nA in average, and an energy up to 150MeV, is planned to be sited at the Frascati ENEA Research Center, in Italy. The accelerator is composed of a sequence of linear sections. The first one is a commercial 7MeV proton linac, from which the beam is injected in a SCDTL (Side Coupled Drift Tube Linac) structure reaching the energy of 52MeV. Then a conventional CCL (coupled Cavity Linac) with side coupling cavities completes the accelerator. The linear structure has the important advantage that the main radiation losses during the acceleration process occur to protons with energy below 20MeV, with a consequent low production of neutrons and secondary radiation. From the radiation protection point of view the source of radiation for this facility is then almost completely located at the final target. Physical and geometrical models of the device have been developed and implemented into radiation transport computer codes based on the Monte Carlo method. The scope is the assessment of the radiation field around the main source for supporting the safety analysis. For the assessment independent researchers used two different Monte Carlo computer codes named FLUKA (FLUktuierende KAskade) and MCNPX (Monte Carlo N-Particle eXtended) respectively. Both are general purpose tools for calculations of particle transport and interactions with matter, covering an extended range of applications including proton beam analysis. Nevertheless each one utilizes its own nuclear cross section libraries and uses specific physics models for particle types and energies. The models implemented into the codes are described and the results are presented. The differences between the two calculations are reported and discussed pointing out disadvantages and advantages of each code in the specific application.

Monte Carlo simulations of the particle transport in semiconductor detectors of fast neutrons

Several Monte Carlo all-particle transport codes are under active development around the world. In this paper we focused on the capabilities of the MCNPX code (Monte Carlo N-Particle eXtended) to follow the particle transport in semiconductor detector of fast neutrons. Semiconductor detector based on semi-insulating GaAs was the object of our investigation. As converter material capable to produce charged particles from the (n, p) interaction, a high-density polyethylene (HDPE) was employed. As the source of fast neutrons, the 239Pu–Be neutron source was used in the model. The simulations were performed using the MCNPX code which makes possible to track not only neutrons but also recoiled protons at all interesting energies. Hence, the MCNPX code enables seamless particle transport and no other computer program is needed to process the particle transport. The determination of the optimal thickness of the conversion layer and the minimum thickness of the active region of semiconductor detector as well as the energy spectra simulation were the principal goals of the computer modeling. Theoretical detector responses showed that the best detection efficiency can be achieved for 500μm thick HDPE converter layer. The minimum detector active region thickness has been estimated to be about 400μm.

Correlated gammas using CGM and MCNPX

Transport codes like MCNPX (Monte Carlo N-Particle eXtended) which are based primarily on experimentally derived data libraries at energies below approximately 100 MeV are reliable and predictive in transporting and producing neutrons and gammas. However, they are deficient in the microscopic sense because of the inability to produce correlated secondary particles. Neutrons will produce the average number of gammas at each collision regardless of the specific neutron reaction. Consequently, capture gammas may be produced by elastic collisions and inelastic gammas may be produced by capture. To remedy this deficiency the Cascading Gamma-ray and Multiplicity (CGM) V3.4 code has been integrated into MCNPX V2.7.0. The CGM code is based on Hauser–Feshbach and optical models. This paper details an overview of the CGM code integration into MCNPX followed by a test case highlighting the gamma spectrum and multiplicities from the CGM/MCNPX code. The test case provides gamma spectrum and multiplicities for the (n,γ) reaction on 56Fe using thermal neutrons. A second test case highlights gamma correlation for the (n,γ) reaction on 56Fe using thermal neutrons using three coincidence detectors.

Construction of boundary-surface-based Chinese female astronaut computational phantom and proton dose estimation.

With the rapid development of China's space industry, the importance of radiation protection is increasingly prominent. To provide relevant dose data, we first developed the Visible Chinese Human adult Female (VCH-F) phantom, and performed further modifications to generate the VCH-F Astronaut (VCH-FA) phantom, incorporating statistical body characteristics data from the first batch of Chinese female astronauts as well as reference organ mass data from the International Commission on Radiological Protection (ICRP; both within 1% relative error). Based on cryosection images, the original phantom was constructed via Non-Uniform Rational B-Spline (NURBS) boundary surfaces to strengthen the deformability for fitting the body parameters of Chinese female astronauts. The VCH-FA phantom was voxelized at a resolution of 2 × 2 × 4 mm3for radioactive particle transport simulations from isotropic protons with energies of 5000–10 000 MeV in Monte Carlo N-Particle eXtended (MCNPX) code. To investigate discrepancies caused by anatomical variations and other factors, the obtained doses were compared with corresponding values from other phantoms and sex-averaged doses. Dose differences were observed among phantom calculation results, especially for effective dose with low-energy protons. Local skin thickness shifts the breast dose curve toward high energy, but has little impact on inner organs. Under a shielding layer, organ dose reduction is greater for skin than for other organs. The calculated skin dose per day closely approximates measurement data obtained in low-Earth orbit (LEO).

Experimental evaluation of a boron-lined parallel plate proportional counter for use in nuclear safeguards coincidence counting

Boron-lined proportional technologies are increasingly being considered as a viable option for the near-term replacement of 3He-based technologies for use in international nuclear safeguards neutron detection and coincidence counting applications. In order to determine the applicability and feasibility of any replacement technology for international safeguards, it must be evaluated against performance parameters specific to nuclear safeguards applications. In this paper, we present an experimental evaluation of a boron-lined parallel plate proportional counter developed by Precision Data Technology, Inc. (PDT). The counter performance was evaluated using a high-rate 252Cf spontaneous fission neutron source and a set of 137Cs gamma-ray sources with a dose rate of 450mR/h at the detector face. The performance data were subsequently compared with an equivalent 3He-based system defined using the Monte Carlo N-particle eXtended (MCNPX) radiation transport code.

Characteristics of the KIGAM long-counter for the neutron energy range below 2.5 MeV

The long-counter is well known as a fluence meter to measure fast neutrons with the wide energy range. Korea Institute of Geoscience and Mineral Resources (KIGAM) has designed a long-counter and made it on the basis of work optimized using Monte Carlo N-Particle eXtended (MCNPX) simulations. Parameters such as the depth of the hole, the number of holes in the modulator, and the gas pressures of 3He were optimized. When the long-counter consisted of a high-density Polyethylene (HD PE) with a diameter of 42 cm and a length of 42.3 cm and a 3He detector with a 3He gas pressure of 4 atm, its intrinsic efficiency was experimentally found to range from 0.045 to 0.051 in the neutron energy range below 2.5 MeV. Its effective length was also measured to be 6.71 + 3.28 × 10−3 × E (keV). The simulation result and the experimental result for the efficiency showed the same trend. When the experimental efficiency for the same counter was compared with that measured at the Japan Atomic Energy Agency (JAEA) to reconfirm its value, agreements with differences from 5% to 14% at neutron energies of 144 keV, 250 keV, and 565 keV were observed.

Sensitivity to Nuclear Data in the Radioprotection Design of the LIPAC (IFMIF/EVEDA) Beam Dump

Linear IFMIF Prototype Accelerator (LIPAC) is the prototype accelerator of the Engineering Validation and Engineering Design Activities (EVEDA) phase of the International Fusion Materials Irradiation Facility (IFMIF) project. The EVEDA phase is a first IFMIF step devoted to the construction of prototypes of the main units. The deuteron beam of LIPAC (125 mA, 9 MeV) is stopped by a conical copper beam stop, giving rise to neutron and photon sources that must be shielded to comply with dose requirements. A reliable characterization of these secondary sources is a mandatory task.The built-in-semi-analytical nuclear models used by advanced Monte Carlo transport codes as Monte Carlo N-Particle eXtended (MCNPX) or Particle and Heavy Ion Transport code System (PHITS) have been demonstrated as unreliable for describing deuteron interactions and secondary particle production at these low energies. The use of reliable external nuclear data is consequently necessary in the design of the LIPAC shielding. In particular, the TENDL-2010 library has been compared with recently published experimental data demonstrating its reliability for deuteron interaction on copper at 9 MeV. The Monte Carlo Universidad Nacional de Educación a Distancia (MCUNED) code has been developed to make use of external nuclear data, and its use with the TENDL-2010 library has proven very satisfactory for LIPAC radioprotection analysis.The impact on radioprotection tasks in LIPAC when the unreliable nuclear models mentioned above are used is discussed.

TU-E-BRB-07: An EPID Based Dosimetric Verification Tool for SBRT with High Dose Rate FFF Beams.

The increasing use of unflattened high dose rate and/or small sized fields in stereotactic body radiosurgery (SBRT) presents a significant challenge and calls for new tools for dosimetric measurements and quality assurance (QA). The purpose of this work is to investigate a high spatial resolution (0.2mm) and high frame rate (50Hz) amorphous silicon flat-panel electronic portal imaging device (EPID) from Perkin Elmer for SBRT. A Monte Carlo N-Particle eXtended (MCNPX) simulation and convolution based calibration procedure has been developed to derive a voxel-based response function specific to the EPID construct and beam characteristics. Both standard photon beams and flattening filter free (FFF) beams of all energies from Varian TrueBeam STX were studied and the linearity and dose rate dependence were tested. EPID with detailed materials composition was simulated using the MCNPX to generate a scatter kernel composed of dose deposition in the EPID phosphor, and optical photon spreading and to deconvolve the EPID images to high spatial resolution photon fluence map. The fluence map was convolved with MCNPX generated kernels to the 3D dose distribution in the phantom and compared with pinpoint ion chamber and film measurements. EPID response showed excellent linearity (R2>0.9998) and dose rate dependence less than 1.8% for up to 2400MU/min. Output factors for field sizes ranging from 1×1 to 20×20cm2 were measured and used to fit the optical photon glare kernel. Fluence profiles deconvolved using MCNPX scattering kernel agrees with the measurements to within 2%. Results of typical pre-treatment QA test exhibit excellent spatial resolution required for SBRT. The high spatial resolution and high frame rate EPID proved to be an accurate and efficient tool for SBRT QA. Through convolution with MCNPX scattering core and comprehensive EPID calibration, accurate 3D dose maps can be generated for independent dosimetric verification of SBRT treatments.

Extension of RPI-adult male and female computational phantoms to obese patients and a Monte Carlo study of the effect on CT imaging dose

Although it is known that obesity has a profound effect on x-ray computed tomography (CT) image quality and patient organ dose, quantitative data describing this relationship are not currently available. This study examines the effect of obesity on the calculated radiation dose to organs and tissues from CT using newly developed phantoms representing overweight and obese patients. These phantoms were derived from the previously developed RPI-adult male and female computational phantoms. The result was a set of ten phantoms (five males, five females) with body mass indexes ranging from 23.5 (normal body weight) to 46.4 kg m−2 (morbidly obese). The phantoms were modeled using triangular mesh geometry and include specified amounts of the subcutaneous adipose tissue and visceral adipose tissue. The mesh-based phantoms were then voxelized and defined in the Monte Carlo N-Particle Extended code to calculate organ doses from CT imaging. Chest–abdomen–pelvis scanning protocols for a GE LightSpeed 16 scanner operating at 120 and 140 kVp were considered. It was found that for the same scanner operating parameters, radiation doses to organs deep in the abdomen (e.g., colon) can be up to 59% smaller for obese individuals compared to those of normal body weight. This effect was found to be less significant for shallow organs. On the other hand, increasing the tube potential from 120 to 140 kVp for the same obese individual resulted in increased organ doses by as much as 56% for organs within the scan field (e.g., stomach) and 62% for those out of the scan field (e.g., thyroid), respectively. As higher tube currents are often used for larger patients to maintain image quality, it was of interest to quantify the associated effective dose. It was found from this study that when the mAs was doubled for the obese level-I, obese level-II and morbidly-obese phantoms, the effective dose relative to that of the normal weight phantom increased by 57%, 42% and 23%, respectively. This set of new obese phantoms can be used in the future to study the optimization of image quality and radiation dose for patients of different weight classifications. Our ultimate goal is to compile all the data derived from these phantoms into a comprehensive dosimetry database defined in the VirtualDose software.

Comparison of fresh fuel experimental measurements to MCNPX calculations using self-interrogation neutron resonance densitometry

A new non-destructive assay technique called Self-Interrogation Neutron Resonance Densitometry (SINRD) is currently being developed at Los Alamos National Laboratory (LANL) to improve existing nuclear safeguards measurements for Light Water Reactor (LWR) fuel assemblies. SINRD consists of four 235U fission chambers (FCs): bare FC, boron carbide shielded FC, Gd covered FC, and Cd covered FC. Ratios of different FCs are used to determine the amount of resonance absorption from 235U in the fuel assembly. The sensitivity of this technique is based on using the same fissile materials in the FCs as are present in the fuel because the effect of resonance absorption lines in the transmitted flux is amplified by the corresponding (n,f) reaction peaks in the fission chamber. In this work, experimental measurements were performed in air with SINRD using a reference Pressurized Water Reactor (PWR) 15×15 low enriched uranium (LEU) fresh fuel assembly at LANL. The purpose of this experiment was to assess the following capabilities of SINRD: (1) ability to measure the effective 235U enrichment of the PWR fresh LEU fuel assembly and (2) sensitivity and penetrability to the removal of fuel pins from an assembly. These measurements were compared to Monte Carlo N-Particle eXtended transport code (MCNPX) simulations to verify the accuracy of the MCNPX model of SINRD. The reproducibility of experimental measurements via MCNPX simulations is essential to validating the results and conclusions obtained from the simulations of SINRD for LWR spent fuel assemblies.

The effect of rib and lung heterogeneities on the computed dose to lung in Ir-192 High-Dose-Rate breast brachytherapy: Monte Carlo versus a treatment planning system

This study investigates to what extent the dose received by lungs from a commercially available treatment planning system, Ir-192 high-dose-rate (HDR), in breast brachytherapy, is accurate, with the emphasis on tissue heterogeneities, and taking into account the presence of ribs, in dose delivery to the lung. A computed tomography (CT) scan of a breast was acquired and transferred to the 3-D treatment planning system and was also used to construct a patient-equivalent phantom. An implant involving 13 plastic catheters and 383 programmed source dwell positions were simulated, using the Monte Carlo N-Particle eXtended (MCNPX) code. The Monte Carlo calculations were compared with the corresponding commercial treatment planning system (TPS) in the form of percentage isodose and cumulative dose-volume histogram (DVH) in the breast, lungs, and ribs. The comparison of the Monte Carlo results and the TPS calculations showed that a percentage of isodose greater than 75% in the breast, which was located rather close to the implant or away from the breast curvature surface and lung boundary, were in good agreement. TPS calculations overestimated the dose to the lung for lower isodose contours that were lying near the breast surface and the boundary of breast and lung and were relatively away from the implant. Taking into account the ribs and entering the actual data for breasts, ribs, and lungs, revealed an average overestimation of the dose by a factor of 8% in the lung for TPS calculations. Therefore, the accuracy of the TPS results may be limited to regions near the implants where the treatment is planned, and is a more conservative approach for regions at boundaries with curvatures or tissues with a different material than that in the breast.

Detection of fast neutrons using detectors based on semi-insulating GaAs

Detectors with AuZn square Schottky contact of the area of 2.5 × 2.5 mm2 were fabricated. On the back side, the whole area AuGeNi eutectic ohmic contact was evaporated. The thickness of the base material (semi-insulating GaAs) was 220 μm. The connection of 4 detectors in parallel was tested to get the detection area of 25 mm2. The 239Pu-Be fast neutron source with energies between 0.5 and 12 MeV was used in experimental measurements. We have investigated the optimal thickness of HDPE (high-density polyethylene) conversion layer for fast neutron detection. The spectra of the neutrons were measured by detectors covered by HDPE converter of different thicknesses. The fast neutron detection efficiency proved experimentally was compared with results from simulations performed by MCNPX (Monte Carlo N-Particle eXtended) code.

Monte Carlo Simulation of Performance of a Time-Resolved Range Telescope Using Selected Image Quality Assurance Phantoms

The superior dose conformation from protons is attributed to the Bragg peak near the end of the proton range. One challenge in proton cancer treatment is to assess the proton range fluctuations due to organ motion such as respiration. A time-resolved proton range telescope that measures coordinates, direction cosines, and the residual range of each proton can be useful in detecting and quantifying variations in radiological path length during the course of proton radiotherapy. In this paper, the Monte Carlo N-Particle eXtended (MCNPX) code was used to simulate the range telescope and study the image quality. To validate the MCNPX simulations, a simulated proton radiograph was compared with an experimentally acquired film for the same phantom. In addition, four quality assurance phantoms were simulated to investigate the quality of simulated proton radiography. Finally, the methods were applied to one phase of a patient four-dimensional computed tomography (4DCT) data set for proton radiography simulations. The results indicate that Monte Carlo simulations offer data that are useful in analyzing image spatial and temporal resolutions. Simulations show that it is useful to quantify the tumor position changes due to respiration by using a proton telescope.

TH‐A‐214‐04: Impact of Body Size of Obese Patients on PET/CT Dose Estimates: Monte Carlo Calculations Using a Set of BMI‐Adjustable Phantoms

Purpose: To assess the effect of obese patientˈs body mass index (BMI) on organ doses from CT and PET exams. Methods: A set of 5 computational phantoms with different BMIs were created for PET and CT dose calculations using the Monte Carlo N‐Particle Extended (MCNPX) code. The phantoms represent patients having a BMI ranging from 23 (normal weight) to 44 (morbidly obese) with increasing amounts of subcutaneous and visceral fat. The external CT dose calculations assumed a whole‐body, diagnostic scan with a GE LightSpeed 16 scanner operating at a tube voltage of 120 kVp. The internal PET dose was based on S‐values for F‐18 and the ICRP‐106 FDG biokinetic model. Results: For the same tube current, ratios of the morbidly obese phantom CT organ doses compared to the normal weight phantom ranged from 0.46∼1 with an average of 0.7 because of shielding by the extra fat. This effect was greatest for deep organs in the abdomen (e.g. colon, lungs, stomach, liver, urinary bladder). For the same injected radioactivity, the average PET organ dose ratios were 0.95 and 0.65 for source organs (e.g. brain, heart, liver, urinary bladder) and organs in the remainder, respectively (e.g. colon, stomach, spleen, etc.). These PET dose differences are due primarily to the obese phantomˈs smaller remainder source S‐values which arise from the addition of the extra fat to the remainder compartment. Conclusions: After adjusting for the increased tube current and tube voltage, the results suggest that obese patients can receive higher absorbed dose to some organs, depending on the protocols. This work, as part of the VirtualDose software development, demonstrates the ability to improve the estimate of organ doses from PET and CT scans for obese patients and will be useful to on‐going efforts to optimize image quality and imaging doses.

TH-E-220-01: Applications of Proton Radiography to Image Guided Proton Therapy - A Monte Carlo Study Involving the Most Likely Path Algorithm

Purpose: To optimize, through Monte Carlo simulation, a protonimagingsystem in localization of lungtumor motion and in quantification of proton range variations for image‐guidedproton therapy. Methods: The protonimagingsystem modeled consists of position detectors and a range telescope. The Monte Carlo N‐Particle eXtended (MCNPX) code with a particle‐tracking feature was used to evaluate imagingsystem performance in visualizing and quantifying proton radiological pathlength variations during respiration. Various proton path approximation algorithms were evaluated to improve the image quality and the optimal Most Likely Path (MLP) algorithm was selected. Tumor trajectories from protonradiographs were computed to image the real‐time respiratory phases and to provide feedback for gated treatment. The dosimetric gain of image‐guided gating treatment was quantified by calculating the equivalent uniform dose (EUD) and normal tissue complication probability (NTCP) of organs at risk (OARs). Results: Image quality of protonradiograph with spatial resolution of ∼ 1.1 mm and range resolution of < 1 mm was achieved by applying the optimal MLP algorithm. Protonradiographs of two patient cases were reconstructed to determine tumor trajectories and radiological pathlength variations. The extracted tumor trajectories were within 1 mm of ground truth as determined from 4DCT. Utilizing tumor tracking, the margin was reduced for gated therapy. The dosimetric analysis shows that with image guidance, the EUD of OARs reduced by as much as 11 % and corresponding NTCP of organs at risk (OARs) reduced up to 16.5%. In our exploratory cases, we see potential gains from using protonradiography for lungcancer treatments. Conclusions: Simulation of protonradiograph suggests that protonimagingsystem can detecttumor motion and provide useful feedback information for gated treatment. The protonimagingsystem is potentially clinical useful for every‐day image‐guidedproton therapy to achieve better clinical outcome.

Comparison of fluence-to-dose conversion coefficients for deuterons, tritons and helions

Secondary radiation in aircraft and spacecraft includes deuterons, tritons and helions. Two sets of fluence-to-effective dose conversion coefficients for isotropic exposure to these particles were compared: one used the particle and heavy ion transport code system (PHITS) radiation transport code coupled with the International Commission on Radiological Protection (ICRP) reference phantoms (PHITS-ICRP) and the other the Monte Carlo N-Particle eXtended (MCNPX) radiation transport code coupled with modified BodyBuilder™ phantoms (MCNPX-BB). Also, two sets of fluence-to-effective dose equivalent conversion coefficients calculated using the PHITS-ICRP combination were compared: one used quality factors based on linear energy transfer; the other used quality factors based on lineal energy (y). Finally, PHITS-ICRP effective dose coefficients were compared with PHITS-ICRP effective dose equivalent coefficients. The PHITS-ICRP and MCNPX-BB effective dose coefficients were similar, except at high energies, where MCNPX-BB coefficients were higher. For helions, at most energies effective dose coefficients were much greater than effective dose equivalent coefficients. For deuterons and tritons, coefficients were similar when their radiation weighting factor was set to 2.

Proton radiography and fluoroscopy of lung tumors: a Monte Carlo study using patient-specific 4DCT phantoms.

Monte Carlo methods are used to simulate and optimize a time-resolved proton range telescope (TRRT) in localization of intrafractional and interfractional motions of lung tumor and in quantification of proton range variations. The Monte Carlo N-Particle eXtended (MCNPX) code with a particle tracking feature was employed to evaluate the TRRT performance, especially in visualizing and quantifying proton range variations during respiration. Protons of 230 MeV were tracked one by one as they pass through position detectors, patient 4DCT phantom, and finally scintillator detectors that measured residual ranges. The energy response of the scintillator telescope was investigated. Mass density and elemental composition of tissues were defined for 4DCT data. Proton water equivalent length (WEL) was deduced by a reconstruction algorithm that incorporates linear proton track and lateral spatial discrimination to improve the image quality. 4DCT data for three patients were used to visualize and measure tumor motion and WEL variations. The tumor trajectories extracted from the WEL map were found to be within 1 mm agreement with direct 4DCT measurement. Quantitative WEL variation studies showed that the proton radiograph is a good representation of WEL changes from entrance to distal of the target. MCNPX simulation results showed that TRRT can accurately track the motion of the tumor and detect the WEL variations. Image quality was optimized by choosing proton energy, testing parameters of image reconstruction algorithm, and comparing to ground truth 4DCT. The future study will demonstrate the feasibility of using the time resolved proton radiography as an imaging tool for proton treatments of lung tumors.

SU‐GG‐T‐419: Modeling Multiple Coulomb Scattering in Therapeutic Proton Beams: A Comparison of Two Algorithms

Purpose: Accurate modeling of multiple Coulomb scattering (MCS) of heavy charged particles is imperative to achieve accurate dose distributions for proton therapy simulations. The Gaussian approximation based on Rossi's theory used in the Monte Carlo N Particle extended (MCNPX) code overestimates the characteristic scattering angle for thin materials. The purpose of this research was to evaluate a new, more accurate MCS algorithm based on Moliere theory that has been implemented in MCNPX. Method and Materials: Simulations of a proton beam with a range in water of 16.1 cm incident on steel spheres of diameters 6.4 mm, 9.5 mm, and 15.9 mm were run and compared to previous simulations completed with the old algorithm and to measured data. Simulated dose was tallied in air at the locations of the film measurements, which were 2 cm, 15 cm, 30 cm, and 63 cm distal to the spheres. Results: When compared to the old MCS algorithm, the new MCS algorithm more accurately modeled the maximum dose enhancement due to scattering 58% of the time and the maximum dose shadow due to scattering 83% of the time. Visual inspection of the dose profiles distal to the steel spheres reveals the consistent improvement in the dose distribution resulting from the new algorithm. Conclusion: The new MCS algorithm appears to be more accurate than the old algorithm. In order to further characterize the algorithm's performance, additional simulations with a simpler geometry and comparisons with measurements are required.

Development of a multi-spectral, multi-geometry computational model for X-ray breast imaging

The introduction of novel applications in X-ray breast imaging warrants new research for image acquisition optimisation. A simulation model was developed to investigate the influence of different imaging techniques and acquisition parameters. It was modelled in Monte Carlo N-Particle Extended and contains an X-ray tube with photon production, a breast model and antiscatter grid model. This paper describes the simulation model, compares the results with experimental and literature data and presents the influence of breast and antiscatter grid parameters on scatter radiation.

X-ray fluorescence Kα/Kβ ratios for a layered specimen: Comparison of measurements and Monte Carlo calculations with the MCNPX code

This paper shows how the Monte Carlo N-Particle eXtended (MCNPX) computer code can easily be applied to calculate the Kα/Kβ ratios of elements distributed heterogeneously in an analyzed specimen. Experiments were performed on specimens made of thick substrates covered by one or two mono-elemental layers (Ti, Ni, and Cu) of intermediate thickness. The Kα/Kβ ratios of the elements present in a substrate and in the layers were measured and then compared with the ratios obtained with the MCNPX computer code and with simple analytical calculations. Good correspondence was achieved between the experimental and calculated values. It was demonstrated that the MCNPX code makes it possible to predict the Kα/Kβ ratios for a specimen composed of layers and a substrate. This code can be applied for recognizing sample homogeneity or the depth heterogeneity of a specimen. In addition, the depth distribution of elements can be estimated and then the coating thicknesses in layered samples can also be determined.